1. Field of the Invention
This invention relates to the application of metal coatings to substrates, and particularly to the application of coatings of oxide dispersion strengthened (ODS) metals to a metal substrate, such as the application of a coating which is compatible with liquid and gaseous oxygen to a metal substrate. Such coatings rate suitable for utility in propulsion systems employing liquid oxygen fuel, such as in oxygen turbopumps, and for contact surfaces in liquid oxygen/gaseous oxygen (LOX/GOX) applications such as vacuum pumps for the manufacture of liquid oxygen. Further, the application of such coatings offers the opportunity for repair of substrates of wrought oxide dispersion strengthened metals.
2. Description of the Prior Art
New and better alloys are sought for the advancement of technologies in propulsion systems and associated hardware for aerospace activities. For example, a need exists for improved materials for contacting surfaces in high speed turbopumps for rocket engines and advanced engines which utilize liquid oxygen fuels. Limiting factors for the materials used in such applications include frictional heating, especially in an oxygen atmosphere. Various alloys have been tested for use and evaluated for their propensity to ignite due to frictional heating, and it has been shown that most alloys will ignite and bum when rubbed together at very high pressure and speed in an oxygen atmosphere. Selection of suitable alloys is also dependent upon the basic properties of the material, such as strength, creep resistance, oxidation resistance, coefficient of expansion, hardness, and ease of machinability to the appropriate configuration, etc. For this reason, the use of coated bearing and shaft surfaces has been attempted to prevent ignition of LOX/GOX incompatible substrates. One such choice of materials is the combination of Monel K-400 and silver, due to their good LOX/GOX compatibility.
Another material exhibiting appropriate properties, including LOX/GOX compatibility, is Inconel MA754, a nickel alloy which is dispersion strengthened by yttria (Y.sub.2 O.sub.3). Prior to the present invention, however, no means had been found for the deposition of coatings of dispersion strengthened metals, particularly oxide dispersion strengthened nickel superalloys, on a substrate. Such metals are dependent upon the even distribution of finely divided chemically inert particles, usually oxides. These are added to the metal by powder-metallurgy techniques and are differentiated from precipitates which form by aging of metastable solid solutions. Wrought ODS alloys have very high strength and oxidation resistance at high temperatures, and have found use in the aerospace industry for components of gas turbine engines, etc. However, when such materials are subjected to temperatures at which liquification occurs, the dispersed oxides migrate to the surface, changing the microstructure of the alloy, and essentially altering the properties thereof.